One of the above-mentioned special instances is the conveyor in the semiconductor fabricating system. Grease is not adequate beause it evaporates to deteriorate the lubricating performance and to contaminate the working environment. A common way of coping with this situation has been to coat the raceway surface of the bearing ring, the surf ace of the rolling element, and/or the surface of the cage pocket with soft metal (such as gold, silver, lead, and copper) or solid lubricant (such as carbon and molybdenum disulfide) in the form of film.
The coating film of solid lubricant has the disadvantage of gradually peeling off while the rolling element is rotating or sliding. Although the coating film evolves less dust than the grease, the resulting dust is detrimental to the clean working environment. In addition, the amount of dust increases under the high-load conditions.
The present inventors' experience in coating the bearing ring and cage with a solid lubricant of fluoroplastic containing a binder revealed that this solid lubricant evolves much less dust than the conventional one. Nevertheless, the coating film of this solid lubricant is still subject to peeling and dropping (evolving dust) under a comparatively large axial load. The result of peeling and dropping is the decreased lubricating function and the direct contact between metals, which leads to adhesion, wear, and short life. In addition, with the coating film peeled off or dropped, the bearing is subject to corrosion in a corrosive environment.
It is an object of the present invention to provide a means to reduce the evolution of dust from a rolling bearing, thereby improving its lubricating performance and prolonging its life.